Project Summary Nanoparticle production and use is growing exponentially. Silver nanoparticles (AgNPs) are produced in increasing quantities largely for antimicrobial purposes, in applications that guarantee significant human exposure. Therefore, it is critical to elucidate any potential human health hazards. Indeed, research to date has demonstrated that AgNPs are among the most toxic nanoparticles tested, perhaps not surprising given their intended biocidal application. However, the mechanism of toxicity of AgNPs is not fully resolved, and little effort has been spent addressing the possibility that certain genetic backgrounds may predispose some individuals to increased risk. In this project, we will test the hypothesis is that an important mode of action of AgNPs is mitochondrial toxicity. The rationale for this hypothesis is that many antimicrobial agents also exert mitochondrial toxicity, because mitochondria are derived from bacteria. Furthermore, the possibility that this is also true of AgNPs is supported by a number of relatively nonspecific assays of mitochondrial function reported in the literature, and by our own preliminary data. Testing this hypothesis is critical for human health because if AgNPs cause significant mitochondrial toxicity, it is likely that deficiencies in human disease genes critical for mitochondrial homeostasis will result in increased vulnerability to AgNP toxicity. Finally, we will test this hypothesis using a range of AgNPs that vary in size, coating, and surface charge.